Telephone central-station s



(Np Mode l.)

G. K. THOMPSON. TELEPHONE CENTRAL STATION SIGNALING GIRGUIT.

No, 587,467. Patented Aug. 3,1897.

F 0!; W Egg UNITED STATES GEORGE K. THOMPSON, OF MALDEN,

PATENT OFFICE.

MASSACHUSETTS, ASSIGNOR TO THE AMERICAN BELL TELEPHONE COMPANY, OFBOSTON, MASSACHUSETTS.

SPECIFICATION forming part of Letters Patent N 0. 587,467, dated August3, 1897.

Application filed May 25, 1897. Serial No. 638,022. (No model.)

To all whom it may concern:

Be it known that I, GEORGE K. THOMPSON, residing at Malden, in thecounty of MiddleseX and State of Massachusetts, have invented certainImprovements in Telephone Central- Station Signaling-Circuits, of whichthe following is a specification.

In the practical operation of telephone-exchange central offices it hasbeen found advisable to employ monitors or supervising operators, whoseduty it becomes to keep a constant watch upon the switchboard operatorsand operationsfor the purposes of detecting any slowness or negligenceon the I 5 part of the said operators in making connections ordisconnections and in responding to signals calling for either operationand of forestalling or remedying the overcrowding with work of anyparticular switchboard operator or section at certain busy hours of theday when the total amount of work might otherwise be unequallydistributed. Means are provided whereby such monitors are enabledreadily and quickly to become apprised of the working condition of thecharge of any switchboard-operator or group of operators.

Thisinvention relates to such means,whieh comprise a supplementary orpilot signal (preferably a special glow-lamp) in an auxiliary localcircuit associated with and common to the several local circuits of theseveral disconnecting-signals of a number of pairs of connection-cords.This pilot-signal is intended for operation whenever any of the in- 3 5dividual disconnecting-signals are actuated, and is adapted to remaindisplayed as long as a single one of such disconnecting-signals isneglected or from any reason is disregarded, and is therefore easily andat once observed by the supervisor, who may proceed to inquire into thereason of the delay. For this purpose it is conveniently placed at someconspicuous part of such portion of the switchboard as it is designed toserve, and, if desired, may be provided with a bulb or globe of specialcolor, in order that it may more readily catch the eye of the person incharge.

The invention is designed for use in connection with common-batterymultiple-switchboard systems wherein the calls and other signals fromthe substations are automatically made by the acts of taking thereceiving-telephone up for use and restoring it to its place again andwherein the substation telephone-transmitters receive theircurrentsupply from a source or generator placed at the central station.

It consists, essentially, in combining the series or group of plug orconnection-cord circuits upon an operators keyboard or switchsection,their respective associated supervisory or disconnecting signals, ashunt-circuit round each signal, an electromagnetic switch controllingthe said shunt, and the supplementary or pilot signal in an auxiliarylocal circuit, with a relay controlling such auxiliarycircuit andpilot-signal and Wound with a plurality of exciting-coils, one for eachconnection-cord or pair of cords, the coil or winding for each cordbeing placed in a second and permanently-closed shunt or derivationround the disconnecting-signal, which second shunt is also controlled,albeit indirectly, by the electromagnetic switch of the first, not,however, in respect to its continuity, but in respect to the passagethrough it of current adapted to excite the relay. By means of the saidmultiple-coil relay and its connections the pilot-signal is operatedefficiently in conjunction with any or all of the disconnecting- 8osignals, and the resistance of each of the multiple windings thereof isof such magnitude that I am enabled to utilize the said windings,respectively, in place of a special resistance in a similar permanentshunt round the disconnecting signal-lamp, which otherwise requires tobe provided to maintain the integrity of the local circuit containingsuch lamp in case the said lamp should burn out or have its conductorbroken and for the ap- 9o propriate operation of any of the well-knownarrangements of multiple-switchboard busytest.Twodisconnecting-signals,oneforeach cord conductor of the pairconstituting the complete connection between the two termi- 5 nal plugs,are generally preferred, and each of these is preferably associated withone of the relay exciting-coils connected with its permanent shunt;butin cases where it is thought sufficient to have the relay and pilotI00 signal worked in conjunction with but one cord of the pair thespecial resistance, of like magnitude with the relay-winding alreadymentioned, may be employed in the permanent shunt round thedisconnecting-lamp of the other cord. Thus in the latter case thewindings of the relay-magnet in the permanent shunt-circuit on one plugside of the connection-cord are each of the same resistance value asthat of the resistance-coil on the opposite plug side of said cord, andin addition to exercising their principal function of excitingmagnet-ism in therelay-core serve also incidentally in the same capacityas do such resistance-coilsviz., to maintain the continuity of thedisconnecting-lamp circuit for testing and such other operations as maybe necessary or convenient should such circuit be from any cause open inthe lamp without interfering with the operativeness of such lamp whenthe same is in order.

The drawing which accompanies this specification is a diagramillustrating the invention as it may be arranged and operated at thecentral station of a telephone-exchange system in association withsubscribers circuits converging thereto.

L and L represent main telephone-circuits converging from substations Aand B to a central station D,where by means of switchboard apparatusthey may be united or connected with any othersubstatiomcircuits, asdesired.

The main telephone-circuits L L have line conductors a (t the former ofwhich is shown as being normally connected to ground G at the substationthrough the hook-switch S and bell d and extends at the central stationthrough the switchboard-sections (being provided in each branchedconnecting-socketj thereat with a spring 11) to the back-stop e of onearmature of the cut-off relay E,which armature has a branch to ground (land continues by an extension through the electromagnet of line-relayEto one pole of battery 5 The conductor 01, (shown as being norm allyopen at the substation) extends through the transmitter M and receiver Tthere placed to the springs 12 in each connecting-socketj of thecentral-station switchboard and to the backstop e of the other armatureof relay E, which armature connects with the remaining pole of batteryI), thus closing the line-circuit at its central-station end.

0 is the call signal-lamp in the normally open local circuit of batteryZ1 controlled by the armature of the relay E v is a wire extending fromground G to the test-rings 13 of each connecting-socket j and in itscircuit including the helices of the relay E.

Each pair of connection-cords is provided with terminal plugs P and l,which are provided with insulated metallic contacts 1, 2, and 3. Thetips 1 of the two plugs are joined by wire f, the sleeves 2 by wire fand the shanks 3 by the wire f The wires f and f are united by thebridge 2'', in the center of which is thetransmitter-battery b placedbetween the electromagnetic resistances or impedance-coils R and R K andK are the supervising or clearingout lamp-signals in their localcircuits on and w,which otherwise may together be regarded as the thirdconductor f of the connectingcord, uniting the contact-surfaces 3 of thetwo plugs thereof. The said local circuits each are adapted to be closedwhen the plugs P P are inserted in the jack-sockets j, and may then foreach plug be traced from ground G through battery I), conductor 91,point z, conductor f plug contact 3, test-rings or socket-trames;13,wireu, cut-off magnet E, to ground at G The disconnecting-signal and thecut-off relay are thus arranged in series in the same local circuit.hen, therefore, the plug P is placed in its socket j, the cutoff relayis operated to sever the normal terminal extension from the maincircuit. The disconnecting-signal is not, however, displayed,

such display being prevented by the apparatus and circuits now to bedescribed. The said disconnectingsignals are provided with normally openshunt-circuits h, which in practice may include a small resistance R asshown in the shunt of lamp K. The said resistance, however, has nointimate relation to this invention and requires no further reference.The said shunts connect with the conductor f at two points 16 17 on thetwo sides of the lamps, and pass from thence through the local points ee of the relays E which local points therefore, together with therelaymagnet and armature, form an electromagnetic switch maintaining theshunt-circuit open as long as the conductor is on open circuit, butclosing the same when by inserting the plug P in a jack representing aclosed line-circuit the battery 5 is enabled to send its current throughthe coils of the relay E The said relay under such conditions becomesexcited and attracts its armature, thus closing the shunt-circuit h andwithdrawing current from the lamps K Kflwhich consequently are notilluminated as long as the shunt-circuit remains closed.

I In the drawing the lamp K is shown as being provided also with apermanently-closed shunt 71, containing a resistance R of about threehundred ohms. This shuntand resistance preserves the continuity of thecircuit when, as sometimes happens, the lamp-filament is burned out orbroken.

The device which forms the essential element or feature of my inventionis shown in the drawing as being particularly associated with thedisconnecting lamp-signal K, although,as hereinbefore explained, it canreadily be applied to both lamps.

F is a relay wound with as many excitingcoils as there are pairs ofplugs and cords at an operators section, say fifteen, each having aresistance of about three hundred ohms, and 3 may represent one end ofeach coil, united at point r to a common wire 13, which IIO is connectedat point 16 on wire f Anextension iof an opposite end of one of thecoils is connected at point 15 to the first shuntcircuit h, and therebyto the armature-lever of the relay E and 41 represents the opposite endsof the other coils, each of which is connected in a similar manner tothe local-circuit conductors of the other cord-circuits. (Not, however,shown.)

C is a local circuit in which is connected the pilot-lamp signal 0 andbattery b, the said circuit being controlled by the relay F, actingthrough its local points c. This circuit can be extended to any desireddistance and to any place, so that the lamp 0 shall be under theattention of the central -.exchange monitor.

The several coils are given a resistance of three hundred ohms each, sothat they may not only exercise their designed function, but maylikewise serve as substitutes for the special resistance R and safeguardthe continuity of the test-circuit without drawing much current from thelamp.

As already suggested, although the signal K is shown as being suppliedwith a special.

resistance R in a shunt, it is preferable that this signal as well as Kshall be provided with an exciting-coil of the pilot-lamp controllingrelay F; otherwise the display of the signal by said lamp K will not beaccompanied by the concomitant display of the pilotsignal. I have,however, shown the said special resistance R mainly as an indicationthat it would be required for continuity-maintaining purposes if themultiple-coil relay F were absent altogether, and that when a coil ofsaid relay is associated with the signals K or K it need not be inaddition to such resistance R but is adapted to be employed as asubstitute therefor.

In the operation of the system when a call is to be made from asubstation the telephone T is removed from the hook-switch S, which,impelled by its spring, closes the main circuit through the telephones.Current from battery btthen excites the relay E whose armature becomesattracted and closes the contacts a of the line-signal local circuit,causing the said'signal 0 to be displayed. The operator thereuponinserts the plug P in the answering-socket j and connects in hertelephone (not shown in the diagram) and receives the call. When theplug is inserted, its tip 1 connects with spring 11, its sleeve 2 withspring 12, and its shank 3 with the ring 13 and a circuit is formed fromground G to the complementary ground G for the current of battery I), ashereinbefore described. The cut-off relay E becomes excited and attractsits two armatures from the contact-points e and c opening the normalmain circuit, demagnetizing the relay E and extinguishing the linelamp-signal o. A portion of the current from the battery 17 tends to bediverted between points 16 and 17 on conductor f by way of thederivation through wire 1), the ap propriate coil of relay F, wire 1point 15, resistance R and conductor a; but when the local points 6 areheld in contact by relay E the amount of current actually passing thatway is negligible. A talking-circuit is also established by theintroduction of the plug into the socket, as follows: from battery 6 byway of retardation-coil R, wire f, tip 1 of plug, spring 11 of socket j,conductor a, switch S, telephones M and T, conductor a spring 12' ofsocket j, sleeve 2 of plug, wire f relay E and retardation-coil R to theother pole of the battery. The current in this circuit of the battery 19excites the relay e thereby operating the electromagnetic switch, whichthe said relay-armature and points constitute, and closing theshunt-circuit it round the disconnecting lamp-signal K, so that themajor part of the current from the battery 6, which splits at point 16,is diverted from the lamp K and also from the relay F and passes throughthe shunt h by way of the contacts 6 and conductor 0, and as suchportion of the current as finds its way through the signal K and throughthe relay-coil is insufficient to light the lamp or excite therelay-magnet the disconnecting and pilot signals remain quiescent. Thesaid lamp and relay both remain shunted and consequently undisplayed aslong as the current from the transmitter supply-battery b circulates inthe main substation-circuit, but when the receiver T is returned to theswitch-support on the conclusion of a conversation the said switch,actuated by the weight of said receiver, opens the line-circuit and thiscurrent is interrupted. The magnet of relay E then loses its excitementand its armature is retracted, operating the electromagnetic switch andopening the shuntcircuit h. There being now no low-resistance path roundthe lamp K and relay-coil, which are in parallel, the former receivessufficient current for its illumination and the relay-coil receivessufficient current for the operative excitation of its core Thus thelamp K displays the signal to disconnect-and the relay F closes thelocal circuit C for the operation ofvthe pilotsignal 0, whereby thelatter is enabled to simultaneously display its signal also.

Since the relay has exciting-coils equal in number to thedisconnecting-signals of the connection-cords with which it isassociated and to which it is common, or to any desired number of suchdisconnecting-signals, it is obvious that Whenever any one of the saiddisconnecting-lamps so associated is lighted current-will flow throughthe corresponding Winding of relay F, which is bridged round such lamp,and that the relayF and the pilot signal 0 controlled thereby willuniformly be operated when any disconnecting-signal is displayed, andwill remain in operation as long as any of the series ofdisconnecting-sig nals remains displayed or is unattended to; and it isalso obvious as the resistance of each of the said exciting-coils of therelay F is substantially the same as that of the shunt resistance R andas the said coils occupy the same relation to the conductor f and theirrespective associated lamps K or K as otherwise would be occupied by thesaid resistances, that they serve not only to excite magnetism in thecores of the relay F, but also serve to maintain the continuity of theirrespective conductors f so that whenever such relay-coils are employedin association with the disconnecting signal lamp the specialcontinuity-preserving resistances may be dispensed with. is indicated bythe broken-line alternative circuit g, which includes one of the coilsof the relay F.

I claim- 1. The combination in a telephone cen tralstation apparatus, ofa series or group of connecting cords or conductors, a correspondingseries of disconnecting lamp-signals, a shuntcircuit round each signal,an electromagnetic switch controlling each shunt-circuit, and a commonsupplementary or pilot signal in an auxiliary local circuit, with arelay controlling such auxiliary local circuit and pilotlamp, and woundwith a plurality of excitingcoils, associated with the said cords anddisconnecting-signals respectively, the said coils or windings beingeach connected in parallel with its associated lamp, and sustaining likerelations with said lamp to the shunt-circuit thereof, and itscontrolling-switch, substantially as described.

2. In a telephone central-station switchboard apparatus, the combinationsubstantially as hereinbefore described, of a group or series of localsignal-circuits; a disconnecting lamp-signal in each; an auxiliary localsignal-circuit; a supplementary or pilot signal common to the saidseries of circuits and lamps contained therein; a relay controlling thesaid auxiliary circuit and pilot-signal, and Wound with a plurality ofindependent magnetizing-coils each associated and connected in parallelwith a corresponding one of said disconnecting lamp-signals; ashunt-circuit round each of the said signals and its associatedrelay-coil; and a main-line relay for each of the said shunt-circuits,forming an electromagnetic switch adapted to open and This function ofthe relay-coil close the same, and thereby control the display andwithdrawal of the disconnecting and pilot signals.

3. The combination in a telephone centralstation switching apparatus,with a plurality or group of disconnecting-signal circuits; alamp-signal in each; a low-resistance shuntcircuit about each signal;and a switch controlling said shunt; of a supplementary signal, commonto and adapted to operate with each and all of the said group ofdisconnecting-signals and their circuits, included in an auxiliarysignal-circuit; and a relay controlling such auxiliary circuit andsignal, and wound with a number of exciting-coils of equal resistance,the said windings being included in a second and permanently-closedshunt-circuit of their associated disconnecting signal-lampsrespectively; substantially as described.

4. The combination in a telephone central station of a series or groupof plug and cord switchboardconductors two disconnecting signal-lampsfor each conductor, one associated with each terminal plug to respond tosignal from a line connected therewith; and two shunt-circuits roundeach lamp, one be ing of low resistance and controlled by anelectromagnetic switch, and the other permanentl y closed and containinga coil having a resistance relatively high to that of the said lamp;with an associated auxiliary circuit and pilot-signal and acontrolling-relay therefor, having a number of exciting-coils, eachinterposed in the said permanently-closed shunt- .cirouit of some one ofthe said disconnecting lamp-signals, and constituting the said coil ofrelatively high resistance, whereby the pilot-signal is enabled tooperate on the operation of any or each of the saiddisconnecting-signals, and whereby the continuity of the lamp-signalcircuit is maintained; substantially as set forth.

In testimony whereof I have signed my name to this specification, in thepresence of two subscribing witnesses, this 18th day of May, 1897.

GEORGE K. THOMPSON.

WVitnesses:

KATHARINE DURFEE, JOSEPH A. GATELY.

